I really enjoyed these specials! Who is fan of the series, surely will like them, too. I suggest watch them after ending the main serie. Not because they will spoiler something, neither because is difficult to understanding, but because: 1 - The first episode is about how the first opening of the anime has been made. 2 - The second one shows Sakura and Tomoyo with the same clothes used by them in the third and last ending video music of the anime, so I guess this episode was created for be a history for that (also counts with the participation of Eriol, who appears only inthe third season of the serie); they are making English cookies, when...
3 - The third one occurs at Tomoeda school and it is about Yamazaki and his lies... in my opinion, this one is the most funny of the specials.

These short episodes are pretty funny, as is a chance to see again the characters (This time on chibi mode! That was so cute *--*) in new adventures. Unmissable. :)